go/types: race condition due to lazy initialization of universeError

[mdempsky]

This program triggers a race condition in go/types on dev.typeparams since 24f9eb2:

package main

import (
	"go/types"
	"sync"
)

func main() {
	var wg sync.WaitGroup

	for i := 0; i < 2; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			types.Universe.Lookup("error").Type().Underlying().(*types.Interface).NumMethods()
		}()
	}

	wg.Wait()
}

/cc @findleyr @griesemer

[findleyr]

@mdempsky thanks for that repro!

This is because we lazily write the interface type set. We should eagerly add an empty type set for interfaces in the universe.

[gopherbot]

Change https://golang.org/cl/336910 mentions this issue: [dev.typeparams] go/types, types2: set tset when constructing interfaces in the universe

[findleyr]

It seems that gopherbot did not find the 'fixes' line on the previous CL, because it was not the first mention of this issue? In any case, closing as fixed.

[zikaeroh]

FWIW, gopherbot did, but GitHub won't close issues via commits until those commits are merged back to the main branch of the repo (so for dev. branches you have to wait or close manually).

[findleyr]

@zikaeroh that makes sense, thanks for the explanation!